1. Field of the Invention
The present invention generally relates to the treatment of waste waters and the like and more particularly to an improved method of neutralizing aldehyde-containing waste waters.
2. Prior Art
Various methods have been used to treat aqueous wastes containing aldehydes in order to neutralize the aldehydes so that the aqueous wastes can then be disposed of without danger to the environment. One such aldehyde frequently encountered is formaldehyde.
Formaldehyde is extensively used in disinfectants and fixatives, usually in 10% aqueous solution in medical facilities. It has also found wide industrial usage as a germicide and embalming fluid. It is also used in the manufacture of artificial silk and other textile fibers, latex, phenolic resins, thiourea resins, malamine resins, dyes, inks, cellulosic esters, mirrors, explosives, etc. It is used in the paper, photographic and furniture industries and as an intermediate in drug and pesticide manufacture.
Waste waters from such processes usually contain appreciable amounts of unreacted formaldehyde, which is a very toxic substance, capable of causing respiratory and digestive disorders and possibly producing carcinogenic effects. Detoxification of those waste waters by neutralizing the formaldehyde is required before the waste waters can be disposed of. Such waste waters typically have an up to about 10 volume % concentration of formaldehyde and a pH of about 2-11.
One conventional process for neutralizing formaldehyde-containing waste waters is set forth in U.S. Pat. No. 3,909,408. The treating agent used is a mixture of sodium sulfite and sodium bisulfite, the latter having the chemical formula NaHSO.sub.3. Such sodium bisulfite by itself has been found to be relatively ineffective as an aldehyde neutralizer, as has sodium sulfite by itself. The process of the patent employs a mixture of these two chemicals for supposedly an improved result. However, that mixture varies, depending on the pH of the waste water to be treated and requires careful attention to details in order to make it work.
One of the problems with the process of the patent is that the sodium bisulfite employed in the patented process produces a hazardous substance, namely, sulfur dioxide, under certain processing conditions, so that the process is complicated and somewhat difficult to carry out successfully. The process employs a step where either the pH of the waste water is initially adjusted, preferably to up to about pH 11, to prevent dangerous off-gassing and/or the relative proportions of its reagents are adjusted.
Therefore, there remains a need for a simple method which has improved efficiency in rapidly and completely neutralizing aldehydes in waste waters and which can eliminate pH adjustment of the waste water before its neutralization, but still can provide a totally aldehyde-neutralized waste water product which is non-toxic and has a pH of about 6-9, usually about 7 and therefore can be disposed of into a sewage drain line without having to adjust the pH. Moreover, such method should employ a treating agent which is easy and safe to store, handle, weigh out and use and which does not off-gas a toxic gaseous product.